Climate change
cut global wheat and corn output by more than 3 percent over the past
three decades compared to growth projections without a rise in
temperatures, a study found on Friday. The impacts translated into up to
20 percent higher average commodity prices, before accounting for other
factors, according to the paper published in the journal Science.

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Crop yields rose over the
period for example as a result of improvements in practices and plant
breeding, and the isolated, negative impact of climate change was
equivalent to about one tenth of those advances.

But that varied widely between countries with Russia, Turkey and Mexico more affected for wheat, for example.

The
isolated impact of climate change on wheat and corn was a warning of
the future food supply and price impact from an expected acceleration in
warming, the paper said.

"Climate
changes are already exerting a considerable drag on yield growth," said
the study titled "Climate Trends and Global Crop Production Since 1980."

The
authors used crop yield models with and without changes in temperature
and rainfall to show global falls in wheat output of 5.5 percent and 3.8
percent for corn as a result of climate change from 1980-2008.

That was equivalent to the entire annual corn crop of Mexico, or the wheat crop of France, the European Union's biggest producer, it said.

Nationally, among the worst affected was Russia, with a nearly 15 percent cull in wheat, while the United States was unaffected.

For
soybeans and rice, climate change winners and losers balanced each
other out. For example, rice gained in cooler, higher latitude
countries.

CO2 The paper, written
by scientists from U.S. institutions including Stanford University and
Columbia University, noted that adaptation responses, such as advances
in crop breeding, could soften the blow of future warming.

"Without
successful adaptation, and given the persistent rise in demand for
maize and wheat, the sizable yield setback from climate change is likely
incurring large economic and health costs," it said.